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How to do dedicated circuits with isolated grounds

I have reviewed manu of the threads in the archives, and if anything I am more confused.

Prior to meeting with our electrician (who likely has no appreciation for audiophile requests), I would love to get some accurate and safe advice as to what I should be asking for.

We have started early construction of a renovation that will include a dedicated audio room. Our 100+ year old home has had it's electrical work modernized years ago with a 200 amp service. Presently, I haven't explored what kind of ground is in place now. Soon we will need to start wiring for the third floor renovation. For the audio room, I was considering having 5 or 6 dedicated 20 amp circuits with isolated grounds. I was thinking that we could run a conduit from our main panel to a subpanel on the 3rd floor (3 floors above the main panel and about 50 feet behind the panel). I guess I would ask the electrical contractor to run the 5 or 6 dedicated circuits from the subpanel. I was thinking of going with 10/3 BX wire for these dedicated circuits and connecting them to PS Audio Power Ports receptacles. Now, my question is what is the electrician supposed to do to create isolated grounds using the 3rd conductor wire in the 10/3 wire. Could someone try to explain to me what is required. Do I need to create another earth ground ? How do I ensure that each dedicated circuit is truly isolated from the others ? Is it necessary for each line to be equal length ?

Could someone explain what is the dirty ground vs. the isolated ground ?

Is it advisable that the other electrical circuits for the 3rd floor (e.g. standard recepacles, lights, etc. run off a second subpanel, or is it OK to have them on the same subpanel as the dedicated circuits ? What about the electrical wiring for our heat pump on the 3rd floor for the 3rd floor HVAC ... any advice ?

Sorry for these questions, but I live in a small city with no recognized audiophile electrical contractors.
thom_y

Showing 1 response by gs5556

gs5556
1,218 posts
 
I did the same type of installation. From the main panel, I installed a 2-pole 100-amp breaker. From this breaker, a run of 1-inch EMT feeder to a 100-amp main-lug sub panel (check with your codes if your sub panel requires a main breaker). The feeder consists of two #3 phase wires, a #3 neutral and a #8 ground. The two phase wires were twisted to minimize common mode noise.

The 100-amp subpanel has a ground bar kit installed. From the sub panel 20-amp breakers, I ran one 10/3 wire to each outlet. The hot/neutral wiring to the outlet was conventional but the green ground wire was attached to the outlet ground screw. The outlet itself was isolated from the box by a plastic strip. (I used BX and metal boxes so I wanted to isolate the BX sheathe from the ground path.)
The nuetral wire from the outlet went to the neutral bar of the sub panel and the ground wire went to the ground bar. The grounds and neutrals are on their own bar - conventionally the G and N's would both go on the neutral bar.

The neutral bar in the subpanel is directly attached to the feeder neutral and the subpanel ground bar is directly attached to the feeder ground conductor - NOT to the bonding fittings. Back at the main panel, the feeder G and N are attached to the neutral bar (no ground bar there - old panel) but it does not matter because the "star" node of the ground is in the subpanel.

Again, check with codes. But my setup has not given me any headaches or hums.
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